The effect of nitric oxide on acetylcholine release in the rabbit bladder

We evaluated the effects of nitric oxide (NO) on acetylcholine release and the contractile response induced by electrical field stimulation in rabbit bladder smooth muscles using a muscle bath and high performance liquid chro matography coupled with microdialysis. Electrical field stimulation (supram aximum voltage, pulse duration 0.5 ms, frequency 5 and 20 Hz) was applied t o a smooth muscle strip isolated from rabbit bladder. With low-frequency (5 Hz) stimulation, pretreatment with N-infinity-nitro-L-arginine (L-NNA) (10 0 muM) significantly increased electrical field stimulation-induced acetylc holine release and contractile response, which were reduced by the addition of L-arginine. Pretreatment with sodium nitroprusside in the absence or pr esence of L-NNA significantly decreased electrical field stimulation-induce d acetylcholine release and contractile response. In contrast, with high fr equency (20 Hz) stimulation, pretreatment with L-NNA and sodium nitroprussi de had no significant effect on either contractile response or acetylcholin e release. Pretreatment with sodium nitroprusside caused no significant cha nges in carbachol and ATP-induced contractile responses. Sodium nitroprussi de and L-NNA had no significant effects on the atropine-resistant part of t he contraction induced by electrical field stimulation in rabbit bladder sm ooth muscles. The results suggest that there is a NO-mediated mechanism inh ibiting acetylcholine release from cholinergic nerve endings in rabbit blad der, which may contribute to bladder function. (C) 2001 Elsevier Science B. V. All rights reserved.